The field of the disclosure relates generally to fuel cell modules and, more particularly, to solid oxide fuel cell modules including staged fuel supply and methods of operation thereof.
Fuel cells convert the chemical energy from a fuel into electricity. They function by electrochemically combining the fuel with an oxidant across an ionic conducting layer. Usually, fuel cells require a continuous source of fuel and oxygen (or air), to sustain the chemical reaction. The fuel is most often hydrogen or a hydrogen-containing composition such as methanol, methane, or natural gas. There are many types of fuel cells, but they all include an anode, a cathode, and an electrolyte that allows ions to move between the two sides of the cell. The anode and cathode contain catalysts that cause the fuel to undergo oxidation reactions that generate ions and electrons. In solid oxide fuel cells, oxygen ions are drawn through the electrolyte from the cathode to the anode. At the same time electrons are drawn from the anode to the cathode through an external circuit, producing electricity.
A typical fuel cell operates at a potential of less than about one (1) Volt. To achieve sufficient voltages for power generation applications, a number of individual fuel cells are integrated into a larger component, i.e., a fuel cell stack. To create a fuel stack, an interconnecting member or “interconnect” is used to connect the adjacent fuel cells together in an electrical series, in such a way that the fuel and oxidants of the adjacent cells do not mix together. A fuel cell stack may consist of hundreds of fuel cells. The amount of power produced by a fuel cell depends upon several factors, such as fuel cell type, cell size, the temperature at which it operates, and the pressure of the gases supplied to the cell. Certain fuel cells, such as solid oxide fuel cells (SOFCs), operate in large-scale power systems that provide electricity to satisfy industrial and municipal needs.
A typical SOFC with internal reforming operates with a large temperature gradient across the cell. However, the electrochemical reactions which power the cell have an optimum temperature which increases the efficiency of the cell. The electrochemical reactions include a reformation reaction that is endothermic and a fuel cell reaction that is exothermic. The fuel cell reaction increases the temperature of the fuel cell unit and the reformation reaction reduces the temperature of the fuel cell unit. The reformation reaction typically is catalyzed at an inlet of the fuel channels while the fuel cell reaction typically is catalyzed along the length of the fuel channels. Thus, the fuel cell unit typically has a cool region at the inlet of the fuel channels and a hot region in the middle or end of the fuel channels. The hot regions typically generate more current than the cool regions, but also experience faster degradation. The uneven temperature distribution throughout the SOFC is caused by the reforming, and fuel cell reactions lead to a non-optimal current distribution and lifespan.
With these concerns in mind, new processes for providing an even temperature gradient across the cell would be welcome in the art. The processes should be able to mechanically provide an even temperature gradient across the cell. The processes should also avoid reducing the power output of the cell. Moreover, it would also be very beneficial if the processes could be implemented with the existing cell structure rather than adding additional components or control procedures.